Osteomyelitis (sometimes abbreviated to OM, and derived from Greek words osteon, meaning bone, myelo- meaning marrow, and -itis meaning inflammation) is infection and inflammation of the bone or bone marrow.[1] It can be usefully subclassified on the basis of the causative organism (pyogenic bacteria or mycobacteria) and the route, duration and anatomic location of the infection.

Contents

Classification[edit]

The definition of OM is broad, and encompasses a wide variety of conditions. Traditionally, the length of time the infection has been present and whether there is suppuration (pus formation) or sclerosis (increased density of bone) is used to arbitrarily classify OM. Chronic OM is often defined as OM that has been present for more than one month. In reality, there are no distinct subtypes, instead there is a spectrum of pathologic features that reflect balance between the type and severity of the cause of the inflammation, the immune system and local and systemic predisposing factors.

Pathogenesis[edit]

In general, microorganisms may infect bone through one or more of three basic methods: via the bloodstream, contiguously from local areas of infection (as in cellulitis), or penetrating trauma, including iatrogenic causes such as joint replacements or internal fixation of fractures or root-filled teeth.[1] Once the bone is infected, leukocytes enter the infected area, and, in their attempt to engulf the infectious organisms, release enzymes that lyse the bone. Pus spreads into the bone's blood vessels, impairing their flow, and areas of devitalized infected bone, known as sequestra, form the basis of a chronic infection.[1] Often, the body will try to create new bone around the area of necrosis. The resulting new bone is often called an involucrum.[1] On histologic examination, these areas of necrotic bone are the basis for distinguishing between acute osteomyelitis and chronic osteomyelitis. Osteomyelitis is an infective process that encompasses all of the bone (osseous) components, including the bone marrow. When it is chronic, it can lead to bone sclerosis and deformity.

Chronic osteomyelitis may be due to the presence of intracellular bacteria (inside bone cells).[2] Also, once intracellular, the bacteria are able to escape and invade other bone cells.[3] At this point, the bacteria may be resistant to some antibiotics.[4] These combined facts may explain the chronicity and difficult eradication of this disease, resulting in significant costs and disability, potentially leading to amputation. Intracellular existence of bacteria in osteomyelitis is likely an unrecognized contributing factor to its chronic form.

Salmonella species are most common in patients with sickle cell disease.[6]

In children, the long bones are usually affected. In adults, the vertebrae and the pelvis are most commonly affected.

Acute osteomyelitis almost invariably occurs in children. When adults are affected, it may be because of compromised host resistance due to debilitation, intravenous drug abuse, infectious root-canaled teeth, or other disease or drugs (e.g., immunosuppressive therapy).

Osteomyelitis is a secondary complication in 1–3% of patients with pulmonary tuberculosis.[1] In this case, the bacteria, in general, spread to the bone through the circulatory system, first infecting the synovium (due to its higher oxygen concentration) before spreading to the adjacent bone.[1] In tubercular osteomyelitis, the long bones and vertebrae are the ones that tend to be affected.[1]

The most common form of the disease in adults is caused by injury exposing the bone to local infection. Staphylococcus aureus is the most common organism seen in osteomyelitis, seeded from areas of contiguous infection. But anaerobes and Gram-negative organisms, including Pseudomonas aeruginosa, E. coli, and Serratia marcescens, are also common. Mixed infections are the rule rather than the exception.[8]

In osteomyelitis involving the vertebral bodies, about half the cases are due to S. aureus, and the other half are due to tuberculosis (spread hematogenously from the lungs). Tubercular osteomyelitis of the spine was so common before the initiation of effective antitubercular therapy, it acquired a special name, Pott's disease.

Diagnosis[edit]

Mycobacterium doricum osteomyelitis and soft tissue infection. Computed tomography scan of the right lower extremity of a 21-year-old patient, showing abscess formation adjacent to nonunion of a right femur fracture.

Diagnosis of osteomyelitis is often based on radiologic results showing a lytic center with a ring of sclerosis.[1]Culture of material taken from a bone biopsy is needed to identify the specific pathogen; alternative sampling methods such as needle puncture or surface swabs are easier to perform, but do not produce reliable results.[10]

Treatment[edit]

Osteomyelitis often requires prolonged antibiotic therapy, with a course lasting a matter of weeks or months. A PICC line or central venous catheter is often placed for this purpose. Osteomyelitis also may require surgical debridement. Severe cases may lead to the loss of a limb. Initial first-line antibiotic choice is determined by the patient's history and regional differences in common infective organisms. A treatment lasting 42 days is practiced in a number of facilities.[11] Local and sustained availability of drugs have proven to be more effective in achieving prophylactic and therapeutic outcomes.[12]

Fossil record[edit]

Evidence for osteomyelitis found in the fossil record is studied by paleopathologists, specialists in ancient disease and injury. It has been reported in fossils of the large carnivorous dinosaur Allosaurus fragilis.[18]